Investigating the Role of Transposons in Temperature-Induced DNA Damage During Spermatogenesis

49 pages. Presented to the Department of Biology and the Robert D. Clark Honors College in partial fulfillment of the requirements for the degree of Bachelor of Science June 2018Meiosis is a specialized form of cell division that sexually reproducing organisms use to generate haploid sex cells. Developing sperm are particularly sensitive to temperature fluctuations, with some studies indicating that exposure to elevated temperature increases DNA damage in spermatocytes, but not oocytes. Although temperature-induced DNA damage has been observed, the underlying molecular mechanisms remain unknown. DNA transposons are mobile genetic elements that produce double-strand DNA breaks (DSBs) when excised from the genome. Additionally, transposons can excise from the genome under heat stress. I hypothesize that heat stress causes transposon excision which may be observed as a linear relationship between transposon copy number and the quantity of DSBs in developing spermatocytes exposed to elevated temperature. To test this hypothesis, I conducted an immunofluorescence screen of wild type Caenorhabditis elegans strains with varying transposon copy numbers. Using deconvolution microscopy, DSBs were visualized via the recombinase RAD-51, a protein involved in the early stages of meiotic DSB repair. Quantification of RAD-51 foci was performed to determine the frequency of temperature-induced DSB formation. My results indicate that Tc1 transposons can excise and insert into the genome after heat shock. Most strains I studied exhibited significant differences in the amount of DNA damage before and after heat shock. Additionally, there seems to be an increase in variability in the amount of DNA damage between the no heat shock and heat shock conditions. Comparisons between Tc1, Tc3, retrotransposons, and DNA transposons, suggests that there is no correlation between transposon copy number and the amount of temperature-induced DNA damage. Taken together, these results indicate temperature-induced DNA damage in spermatocytes has multiple mechanisms, with excision of Tc1 transposons as one possible mechanism